LIVE INTERACTIVE YOUR DESKTOP Thursday, June 12, 2008 NSDL/NSTA Web Seminar: Enlightening Experiences with Energy

John L. Roeder, AAPT Physics Teaching Resource Agent, Physics Teacher, The Calhoun School, New York, NY Today’s NSDL Experts Dr. Cathy Ezrailson, Assistant Professor of Science Education, University of South Dakota, Vermillion, SD

Overview Energy concepts can often be confusing to non-scientists because the word “energy” may be used for different ideas…. Often, energy, power, and work are used interchangeably. Defining energy by how we gain it, use it or lose it can help us to grasp an understanding of what is meant by “energy.”

Teaching About Energy: Designing a Roller Coaster Examples from the Physics Front collection

Suppose you have a choice of two ways to pull a cart to the top of a hill: 1 2 steep slopegentle slope SteepGentleNeither Which way requires you to apply more force? Stamp your answer:

Suppose you have a choice of two ways to pull a cart to the top of a hill: 1 2 steep slope gentle slope SteepGentleNeither Which way requires a greater distance? Stamp your answer:

1 2 steep slope gentle slope x Which of the following would be true? A.Product for steep slope is larger than products of gentle slope. B.Product for gentle slope is larger than products of steep slope. C.Products same for both slopes.

What do you recognize as an important trend in the last column above for all of the data? Force (N)Distance (m)Force x Distance (J) Trials at different heights:

Did you notice that all products of force x distance are very close to the same for all slopes? Force x Distance (J)

Physicists get excited when they find that a combination of variables gives something that is nearly constant Whoo hooo! Sonya Kovalevsky

…AND they give it a special name: WORK --- the product of force x distance The product of the force acting on the cart (in the direction of motion) times the distance it acts equals the work done on the cart. Lise Meitner

When work is done on an object, we say that the object gains energy Since work is done against gravity and the cart has the potential to roll down the hill again, the cart is said to gain gravitational potential energy (GPE)

Let’s pause for questions from the audience….

Try Your Hand in this Work-Energy Simulation: Energy Skate Park

Gravitational potential energy (GPE) comes from the work done to lift the object directly upward. Since the force needed to lift the cart must offset its weight: GPE gain = force (weight) x height gained = mass x g earth x height gained h

Height = 0.24 m Mass = 0.5 kg Earth’s gravity = 10 N/kg The cart gains: 0.5 kg x 10 N/kg x 0.24 m = 1.20 J of GPE. An example…..

Height = 0.24 m Mass = 1.0 kg Earth’s gravity = 10 N/kg Solve the equation in the chat What if we doubled the mass?

1.The work done to lift the cart depends only on its weight and the vertical height gain, not the slope. Special things to note: Work = GPE gain 2.The work done to lift the cart equals the gain in GPE, not the total GPE.

A. GPE decreases, cart gains more energy from the motion it acquires. B. GPE decreases, cart gains energy from its motion, but not as much. C. GPE decreases, cart gains the same amount of energy from its motion. What would happen to the GPE it had gained? Now, suppose you let the cart roll down from the top of the hill…..

Quiz Question On graph: How is the decrease of the cart’s GPE related to the speed it gains? Write your responses in the chat

Answer Speed measured at bottom of hill If the speed of the cart is measured at the bottom of the hill after release from different heights, the graph of decrease in GPE vs. speed squared is found to be a straight line.

The slope of the straight line is half the cart’s mass. Therefore, the GPE decrease = (1/2)mv 2. The quantity (1/2)mv 2 is called the kinetic energy, so named because it is energy associated with motion.

GPE is matched by KE …And, some of the cart’s gravitational potential energy (GPE) can be considered to be converted to kinetic energy (KE).

Unless work is done on an object to increase the object’s energy OR the object does work to increase the energy of another object, the amount of energy of that object stays the same. We say that its energy is conserved. Lisa Randall

Let’s pause for questions from the audience….

In which of the pictures above is the amount of work done to raise the cart from the floor to the top of the step the most? So, in terms of Force and Displacement: A A B B C C

Review The energy of something stays the same unless it does work on something else or something else does work on it. “Using” energy requires converting it into a form we need. But some conversions lead to forms less useful than others.

Thermal energy, the kinetic energy of randomly moving molecules, is less useful than the more orderly motion of electric charge moving in an electric circuit. And although energy can be converted among many forms

While all of the energy in electric charge in a circuit can be converted to thermal energy, only some of the thermal energy can be converted to electric charges in a circuit.

These and Other Resources Can be Found in The Physics Front Digital Library Searchable and peer-reviewed items for Physics and Physical Science K-12 Organized by Course Type and Topic Each of which Contain Units and Unit Elements: –Lesson Plans –Teacher Content Support –Student Tutorials –Assessments –References –Simulations Go to the home page here

Inclined plane interactive

Physics Education Technology (PhET): The Ramp

Different Kinds of Energy

THANK YOU!

Download our Seminar Resource List Utilize our blog featuring our presenters for the Seminar Series sharing their insights on careers in science and science education: Go to and click on the K-12 audience page to:

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National Science Teachers Association Gerry Wheeler, Executive Director Frank Owens, Associate Executive Director Conferences and Programs Al Byers, Assistant Executive Director e-Learning LIVE INTERACTIVE YOUR DESKTOP NSTA Web Seminars Flavio Mendez, Director Jeff Layman, Technical Coordinator